3GPP (the 3rd Generation Partnership Project) is currently standardizing release 10 of the Long Term Evolution (LTE). LTE release 10 and beyond is also referred to as LTE-Advanced.
3GPP LTE release 10 includes support for relays. A relay is an intermediate network node which relays information between one or more mobile terminals, e.g. LTE user equipments (UEs), and another base station, commonly referred to as the donor base station. The donor may be an evolved NodeB (eNB) and may also be referred to as a donor eNB or DeNB. The relay does not have its own fixed backhaul connection, but is instead connected to the core network via a wireless communication link to the donor base station. Thus, relays may be deployed to extend cell coverage, e.g. in areas where no wired backhaul connection is available. The communication link between relay and donor is referred to as the backhaul link, and the link between the relay and a connected mobile terminal is referred to as the access link. The current assumption is that a relay, or relay node (RN) shall have the following characteristics:                It controls one or more cells, in the following referred to as “relay cells”, each of which appears to a user equipment (UE) as a separate cell distinct from the donor cell or cells, i.e. the cells controlled by the donor base station.        The cells controlled by the relay shall have their own physical cell identity, as defined in LTE Rel-8, and the relay node shall transmit its own synchronization channels, reference symbols, etc.        The UE shall receive scheduling information and Hybrid Automatic Repeat request (HARQ) feedback directly from the relay node and send its control signalling (SR/CQI/CSI/ACK) to the relay node.        The additional relay functionality is not expected to impact UEs, and it is required that all legacy LTE UEs can be served by the relay cell.        
Between a relay and its donor eNB, i.e. on the backhaul link, transmissions are done on a radio interface denoted Un. Transmissions between UE and relay, i.e. on the access link, are done over a radio interface denoted Uu, which is the same interface as is used for regular eNB to UE communication. The setup is illustrated in FIG. 1.
If the transmissions on Un, and Uu in the relay cell are performed within the same frequency band, the relay is referred to as an inband relay. In case the transmissions are on separate frequency bands, the relay is referred to as an outband relay.
To enable inband relays to be functional, some relays cannot transmit on the Uu interface and receive on the Un interface at the same time. To do so could cause severe self-interference, since Uu and Un transmissions are performed within the same frequency. For the downlink (DL), to enable the relay to not transmit anything in its own cell, i.e. on the Uu interface, the relay cell configures certain subframes as MBSFN subframes, where MBSFN stands for Multimedia Broadcast over a Single Frequency Network. During an MBSFN subframe, the UEs in the relay cell do not expect to receive any reference signals or DL data from the relay beyond what is transmitted in the first one or two Orthogonal Frequency Division Multiplexing (OFDM) symbols of the subframe. Instead, the relay node listens to the downlink transmissions on the Un interface during the rest of these subframes, which are hence used for carrying downlink data from donor eNB to RNs. This is illustrated in FIG. 2, which shows MBSFN subframes and the corresponding time multiplexed DL transmissions on the Un (DeNB to RN) and Uu (RN to UE) interfaces. Note that at most six subframes in a radio frame can be configured for MBSFN. Subframes [0 4 5 9] cannot be configured for MBSFN, implying that at most six out of the ten subframes in a radio frame can be used for Un transmissions.
Similarly, in the uplink the relay node cannot both listen to the UE's transmissions on the Uu interface and transmit to its donor eNB on the Un interface. However, in the uplink, there is no problem if the relay node temporarily does not listen to the Uu and hence there is no need for a special configuration to enable the relay to “turn away from” the Uu interface. This can instead be handled by not scheduling any data on Uu in the relevant subframes.
In this disclosure, the terms Un and Uu subframes will be used when referring to the transmission on the different links. MBSFN subframes are assumed to be configured in the relay cell to enable the relay to receive from its donor without self-interference from its own transmission to its UEs.
It has been discussed in 3GPP how to configure the Un allocation for the relay node, i.e. the split between time spent listening to Un and time spent transmitting on Uu, and whether a more or less dynamic reconfiguration procedure should be allowed. Some considerations must be taken when doing the Un/Uu subframe configuration:                It takes time to change a Un/Uu subframe configuration because once a decision to change the configuration has been made, it has to be propagated to several nodes and equipments. The main time consumer is that the relay is using an MBSFN configuration on the Uu, and to change that configuration requires that the system information broadcast is changed, so that all UEs assuming a certain MBSFN configuration receive information of the change. It could potentially take several seconds before such a change of system information broadcast is applied in the UEs. During this time, it might not be possible to use the new configuration, or potentially not possible to use all slots of the old configuration.        There needs to be a way to know when the configuration should be changed; it might not be possible for the relay or the donor eNB to make the decision on their own, as they might need input from each other.        It might be beneficial, or even required, for the UL and DL configuration for Un to match each other so that a UL subframe occurs e.g. four subframes after a DL subframe so that the relay can send an Hybrid Automatic Repeat reQuest (HARQ) ACK/NACK report for received DL packets.        
The node controlling the Un/Uu subframe allocation for a relay is likely to be, but is not limited to, the donor eNB or the Operation and Maintenance (OAM) system, or OAM node, in the network. The performance of a relay-enhanced system is quite dependent on the Un/Uu subframe allocations. Alternative configurations can also achieve different things when it comes to capacity, coverage, peak rates etc. The optimal allocation may be different for different relays and for different donor eNBs, and in different radio conditions. However, there is currently no mechanism defined for how the controlling node, e.g. donor eNB, should determine the relay subframe configuration.